Reducing mill



Aug. 20, 1940. w. M. SHELDON REDUCING MII'IL Filed June 2, 1938 2 Sheets-Sheet 1 In; ATTORNEY W. 20, 1940. w. M. SHELDON 82 REDUCING MILL Filed June 2; 193a 2 Sheets-Sheet 2 ATTORNEY' Patented Aug. 20, 1940 REDUCING MILL William M. Sheldon, Roselle Park, N. 1., assignor to Louis Ruprecht; Montclair, N. J.

Application June 2, 1938, Serial No. 211,333

- Claims.

This invention relates to impact-type mills for pulverizing or comminuting moist clay, or ceramic body or other moist materials containing suiiicient moisture to be tacky and too little to be 5 pasty. Clays containing 14 to 22% of moisture have such properties; they can be crumbled in the hand and yet are tacky enough'to stick to a surface if projected against it at any considerable speed. For convenience, the term "moist clay in will be used hereafter to designate such moist materials in general.

More particularly, the invention relates to reducing mills for operating on such material in which the material is fed by suitable means, most 18 desirably by means of a conveyor belt, in a flat layer to the under side of a rotor having a series of circumferentially spaced hammers and mounted horizontally and driven at comparatively high speed so that the hammersstrike the 26 end of the layer in the direction in which the layer is moving and throw, a stream of the comminuted clay in a substantially horizontal direction. The product of reducing mills of this kind is for the most part very uniform and finely 25 comminuted. Some considerable difllculty has been experienced in the operation of such mills, however, from the fact that the product, other-' wise highly satisfactory, has been found at times to contain flakes and lumps of the moist clay or 30 other tacky material of a size entirely disproportionate to the fine" particles constituting the bulk of the product. The presence of these flakes and lumps in the product, I believe to be due to the I fact that some of the clay as it is fed beneath the rotor is beaten down on to the conv yor belt and caused to adherethereto in the f m of a compacted sheet, and that parts of this sheet then flake off as the belt bends downward about its supporting roll and are discharged with the flnely comminuted product; and, further, to the fact that some oversize lumps are struck by the ham-'- mers in such'a way as to be thrownoutwardly with the comminuted product only partially broken up or without having been broken up at all.

The object of the present invention is to prevent the discharge of such flakes or lumps with the finely comminuted product.

To this end, I provide the reducing mill with means whereby a self-adjusting retarding surface of the clay or other material being reduced which Just clears or is scraped by the ends of the I rotor hammers is maintained Just beyond the line of closest approach of the hammer ends and the feed conveyor or other material-supporting means cooperating with the rotor. This selfadjusting retarding surface is obtained by mounting a wide cross-barbeneath the rotor just'beyond the line of closest approach of the hammer ends and the cooperating material-supporting means, extending parallel with the rotor axis 5 and spaced a short distance away from the path of the hammer ends, and so formed that a layer of the clay or other material builds up thereon to an amount permitted by the rotating hammers and is thereafter maintained withan approx- 10 imately zero clearance between its surface and the hammer ends. This retarding device formed by the cross-bar and its accumulated layer of clay or the like is the characterizing feature of reducing mills of the invention. In the operation of the mill provided with such a retarding device, oversize agglomerations of the moist clay or the like are reduced by the rapidly moving hammers by coaction with the closeclearance retarding surface of compacted clay or the like of the retarding device, with the result that the discharged product is without the objectionable flakes or lumps, being composed wholly of particles of the desired small size. I

The retarding device cross-bar is so formed and so positioned that a layer ofthe discharge .material will be built up and maintained thereon extending transversely of the path of movement of the reduced material discharged .by the rotor and extending circumferentially of and parallel to the path of movement of the hammer ends .from a line close to the material feed belt or other material-supporting surface cooperating with the rotor and Just beyond the line of closest approach of the-rotor hammers and the material-support- 3s ing surface. The form of bar I have so far found best has a flat portion facing the rotor and a flange along its far, or outer, upperv edge.

The drawings show illustrative embodiments of the invention in a hammer mill of preferred'con- 40 struction for red cing moist clay and the like.

Fig. 1 is a plan view of the mill with a retarding device of the form now considered best; Fig. ;is a longitudinal sectional view taken on Fig. 3 is a longitudinal sectional view on an enlarged scale of the rotor/ and retarding device and adjacent parts of the feed conveyor; and

Figs. 4 and 5 are views similar to Fig. 3 but showing modified forms of the retarding device.

Referring to the drawings, and first to Figs. 1, 2 and 3, the moist clay mill shown comprises a 'frame III having mounted therein a rotor I l commounted on a central hub on a shaft H by which the rotor is driven in the direction indicated by the arrow. Beneath the roller is a drum or roll l3 supporting one end of a horizontally extending rubber-surfaced conveyor belt I, the other end of which belt is carried by a roll 15, the rolls and belt being driven by roll shaft l3. Above the receiving end of the conveyor belt is a feed hopper H for receiving the moist clay to be comminuted and for depositing it on the feed belt. A rubber surfaced spreading roller 18 rotatably mounted between arms I9 extending forward from a shaft 20 pivotally mounted on the frame l0 above the conveyor belt serves to spread the clay on the belt in a layer of substantially uniform thickness.

Rubber-faced side guides 22 serve to keep the clay from spilling off the belt and to present the clay to the rotor in a layer of such limited width less than the axial length of the rotor that the edges of the layer of clay fed to the rotor shall not extend beyond either end of the rotor, and their end portions toward the rotor are adjustaable laterally with respect to the belt by means of screws 23. The end portions of the guides adjacent the rotor are shaped to flare upwardly.

and outwardly as shown at 22' to catch the clay which may be carried around by the rotor and thrown down toward the edges of the feed belt.

The rotor is enclosed in a housing 25 which extends about thetop, sides and ends of the rotor and has a lining 26 of soft rubber, and the peripheral wall of the casing is curved inward at the end adjacent the feed belt, as indicated at 21, in order to deflect forward the air current within the casing and thus avoid any backwardly directed current of air from strikingthe layer of material being fed forward on the feed belt.

The rotor is driven at relatively high speed so that, as the clay is fed theretoby the hammers and broken up, the comminuted clay is thrown outwardly in a substantially horizontal but somewhat upwardly inclined direction, and at considerable speed. The discharged comminuted material is collected on a rubber surfaced feed,

belt 28 which provides a collecting surface moving away from the rotor in the same general direction as the discharged particles and inclined upwardly at an angle to the horizontal somewhat less than that of the direction in which the particles are discharged by the rotor. The comminuted material will thus strike the collecting surface only after it has commenced to fall by gravity, and, because of the movement of the collecting surface, the relative movement between the collecting surface and the comminuted material at the moment of impact is reduced.

For a rotor having a diameter of 12", a suitable speed of rotation is about 3600 R. P. M., with the feed conveyor spaced about to inch from the peripheral path of the hammer ends and driven at about 25 to 30 feet per minute. The

collecting belt is most desirably driven at about 125 to 150 ft. per minute.

A wide cross-bar 30 is mounted between the side members of the frame l9 to extend parallel with the rotor axis just beyond the line of closest approach of the rotor hammer ends and the feed belt, the feed belt at this line being supported by the roll I3. The bar 30 has at its far, or outer, upper, edge a flange 3! extending toward the rotor, and the surface of the bar facing toward the rotor is spaced somewhat away from the. path of the hammer ends, so that in the operation of the mill comminuted clay will build up on the bar to the thickness permitted by the rotating hammers, thus providing a layer 32 of thedischarged material extending transversely of the path of movement of the material as discharged by the rotor, and extending circumferentially parallel to the path of movement of the hammer ends from close to the material feed belt Just beyond the line of closest approach of the rotor hammers and the feed belt. The flange 3| serves to hold this built-up layer in place on the bar 30. The mill is thus provided with what I have termed a retarding device having a self-adjusting surface of the comminuted material lying across the path of discharge of the comminuted material and extending at approximately zero distance from the path of movement of the ends of the rotor hammers for a short distance circumferentially of the path of movement of the hammer ends from a line close to the feed belt, and this retarding device serves very effectively to prevent the 'discharge of flakes or oversized lumps with the flner comminuted product, as hereinbefore explained.

I have found it most desirable to have the claycollecting surface or the bar 30 about 2" wide and spaced about $41 to inch away from the path of movement of the hammer ends.

Instead of a bar 30 having a flange at its far edge for retaining the built-up layer of clay, a flangeless bar 30a may be used set at an angle as shown in Fig. 4, or a bar 30b extending parallel to the path of the hammer ends and without any retaining flange but having its surface suitably roughened, as by means of perforations therein, as shown in Fig. 5, may be used. These bars of Figs. 4 and 5 will serve to hold the built-up clay layer so that the desired self-adlusting retarding surface is maintained at approximately zero distance from the path of the movement of the hammer ends. A flanged crossbar such as shown in Figs. 2 and 3 is, however, preferred.

What is claimed is v 1. In a mill for reducing moist clay and the like, the combination with a high speed rotor having a series of circumferentially spaced hammers, and means for feeding a layer of the moist. material on a horizontally moving supporting surface to the under side of the rotor, and means for driving the rotor so that its hammers strike the layer of material in the same direction as such layer is moving but at a much greater speed, of a retarding device beneath the rotor and Just beyond the line of closest approach of the ends of the rotor hammers and said material-supporting surface, said retarding device having a surface extending transversely of the path of.

movement of the reduced material discharged by the rotor in position to be struck by some of the discharged reduced material and formed to hold the layer. of the material which builds up thereon, whereby during the operation of the mill a-layer of the reduced material is maintained thereon having a selfeadjusting surface extending parallel to the path of movement of the hammer ends at approximately zero distance therefrom and the inner edge of which is close to said supporting surface.

2. In a mill for reducing moist clay and the like, the combination with a high speed rotor having a series of circumferentially spaced hammers, and means for feeding a layer of the moist material on a horizontally moving supporting surface to the under side of the rotor, and means for driving the rotor so that its hammers strike the layer of material in the same direction as such layer is moving but at a much greater speed, of a retarding device beneath the rotor and 'just beyond the line of closest approach of the ends of the rotor hammers and said material-supporting surface, said retarding device having a surface extending transversely of the path of movement of the reduced material discharged by the rotor in position to be struck by some of the discharged reduced material and having a flange at its far edge to hold the layer of the material which builds up thereon, whereby during the operation of the mill 9. layer of the reduced material is maintained thereon having a selfadjusting surface extending parallel to the path of movement of the hammer ends at approximately zero distance therefrom and the inner edge of which is close to said supporting surface.

3. In a mill for reducing moist clay and the like, the combination with a high speed rotor having a series of circumferentially spaced hammers, and means for feeding a layer of the moist material on a horizontally moving supporting surface to the under side of the rotor, and means for driving the rotor so that its hammers strike the layer of material in the same direction as such layer is moving but at a much greater speed, of retarding means comprising (a) a wide crossbar extending parallel with the rotor axis \beneath the rotor and just beyond the line of closest approach of the ends of the rotor hammers and the material-supporting surface and having a surface facing the rotor and spaced away from the path of the hammer ends with a flange at its far edge extending toward the rotor, and (b) a layer of the reduced material on said bar providing a self-adjusting surface extending parallel to the path of movement of the hammer ends at approximately zero distance therefrom and the inner edge of which is closeto said supporting a surface.

4. In a mill for reducing moist clay and the like, the combination with a high speed rotor having a series of circumferentially spaced hammers, and means for feeding a layer of the moist material on a horizontally moving supporting 5 surface to the under side of the rotor, and means for driving the rotor so that its hammers strike the layer of material in the same direction as such layer is moving but at a much greater speed,

of retarding means beneath the rotor and just 6 beyond the line of closest approach of the ends of the rotor hammers and said material-supporting surface, said retarding means comprising a member whereon a layer of the reduced material is maintained providing a self-adjusting surface 15 extending parallel to the path of movement of the hammer ends at approximately zero distance therefrom and the inner edge of which is close to said supporting surface.

5. In a mill for reducing moist clay and thelgo like, the combination with a high speed rotor;

having a series of circumferentially spaced hammers, and a substantially horizontal belt conveyor for feeding a layer of the moist material to the under side of the rotor, and means for 25 driving the rotor so that its hammers strike the layer of material in the same direction as such layer is moving but at a much greater speed, the conveyor belt being supported beneath the rotor by a roll about which the belt turns down- 0 ward, of a retarding device mounted beneath the rotor and just beyond theline of closest approach of the ends of the rotor hammers and the feed belt comprising a member whereonia layer of the reduced material is maintained providing a 85 w SHELDON. 40 

